When one session SELECT ... FOR UPDATE and holds the lock, subsequent
sessions that SELECT ... FOR UPDATE will wait to get the lock.
Currently, that event is labeled as `wait/io/table/sql/handler`, which
is incorrect. Instead, it should have been
`wait/lock/table/sql/handler`.
Two factors contribute to this bug:
1. Instrumentation interface and the heavy usage of `TABLE_IO_WAIT` in
`sql/handler.cc` file. See interface [^1] for better understanding;
2. The balancing act [^2] of doing instrumentation aggregration _AND_
having good performance. For example, EVENTS_WAITS_SUMMARY... is
aggregated using EVENTS_WAITS_CURRENT. Aggregration needs to be based
on the same wait class, and the code was overly aggressive in label a
LOCK operation as an IO operation in this case.
The proposed fix is pretty simple, but understanding the bug took a
while. Hence the footnotes below. For future improvement and
refactoring, we may want to consider renaming `TABLE_IO_WAIT` and making
it less coarse and more targeted.
Note that newly added test case, events_waits_current_MDEV-29091,
initially didn't pass Buildbot CI for embedded build tests. Further
research showed that other impacted tests all included not_embedded.inc.
This oversight was fixed later.
All new code of the whole pull request, including one or several files
that are either new files or modified ones, are contributed under the
BSD-new license. I am contributing on behalf of my employer Amazon Web
Services, Inc.
[^1]: To understand `performance_schema` instrumentation interface, I
found this URL is the most helpful:
https://dev.mysql.com/doc/dev/mysql-server/latest/PAGE_PFS_PSI.html
[^2]: The best place to understand instrumentation projection,
composition, and aggregration is through the source file. Although I
prefer reading Doxygen produced html file, but for whatever reason, the
rendering is not ideal. Here is link to 10.6's pfs.cc:
https://github.com/MariaDB/server/blob/10.6/storage/perfschema/pfs.cc
* FreeBSD returns errno 31 (EMLINK, Too many links),
not 40 (ELOOP, Too many levels of symbolic links)
* (`mysqlbinlog|mysql`) was just crazy, why did it ever work?
* socket_ipv6.inc check (that checked whether ipv6 is supported)
only worked correctly when ipv6 was supported
* perfschema.socket_summary_by_instance was changing global variables
and then skip-ing the test (because on missing ipv6)
Improve documentation of performance_schema tables by appending COLUMN
comments to tables. Additionally improve test coverage and update corresponding
tests.
report correct error codes in ed25519.
Invalid value stored in the user table or an OpenSSL error is CR_ERROR.
When a user provided incorrect password when logging in -
it's CR_AUTH_USER_CREDENTIALS.
Unfortunate DROP TEMPORARY..IF EXISTS on a regular table may allow
subsequent CREATE TABLE statements to steal away the PFS_table_share
instance from the dropped table.
This allows one to run the test suite even if any of the following
options are changed:
- character-set-server
- collation-server
- join-cache-level
- log-basename
- max-allowed-packet
- optimizer-switch
- query-cache-size and query-cache-type
- skip-name-resolve
- table-definition-cache
- table-open-cache
- Some innodb options
etc
Changes:
- Don't print out the value of system variables as one can't depend on
them to being constants.
- Don't set global variables to 'default' as the default may not
be the same as the test was started with if there was an additional
option file. Instead save original value and reset it at end of test.
- Test that depends on the latin1 character set should include
default_charset.inc or set the character set to latin1
- Test that depends on the original optimizer switch, should include
default_optimizer_switch.inc
- Test that depends on the value of a specific system variable should
set it in the test (like optimizer_use_condition_selectivity)
- Split subselect3.test into subselect3.test and subselect3.inc to
make it easier to set and reset system variables.
- Added .opt files for test that required specfic options that could
be changed by external configuration files.
- Fixed result files in rockdsb & tokudb that had not been updated for
a while.
slave_list was used to provide data for SHOW SLAVE HOSTS and
Slaves_connected status variable.
Introduced binlog_dump_thread_count which is exposed via Slaves_connected
(replaces slave_list.records).
Store Slave_info on THD and access it by iterating server_threads
(replaces slave_list).
Added:
THD::slave_info
binlog_dump_thread_count
show_slave_hosts_callback()
Removed:
slave_list
SLAVE_LIST_CHUNK
SLAVE_ERRMSG_SIZE
slave_list_key()
slave_info_free()
init_slave_list()
end_slave_list()
all_slave_list_mutexes
init_all_slave_list_mutexes()
key_LOCK_slave_list
LOCK_slave_list
Moved:
SLAVE_INFO -> Slave_info
register_slave() -> THD::register_slave()
unregister_slave() -> THD::unregister_slave()
Also removed redundant end_slave() from close_connections(): it is called
again soon afterwards by clean_up().
Pre-requisite for clean MDEV-18450 solution.
Make all system tables in mysql directory of type
engine=Aria
Privilege tables are using transactional=1
Statistical tables are using transactional=0, to allow them
to be quickly updated with low overhead.
Help tables are also using transactional=0 as these are only
updated at init time.
Other changes:
- Aria store engine is now a required engine
- Update comment for Aria tables to reflect their new usage
- Fixed that _ma_reset_trn_for_table() removes unlocked table
from transaction table list. This was needed to allow one
to lock and unlock system tables separately from other
tables, for example when reading a procedure from mysql.proc
- Don't give a warning when using transactional=1 for engines
that is using transactions. This is both logical and also
to avoid warnings/errors when doing an alter of a privilege
table to InnoDB.
- Don't abort on warnings from ALTER TABLE for changes that
would be accepted by CREATE TABLE.
- New created Aria transactional tables are marked as not movable
(as they include create_rename_lsn).
- bootstrap.test was changed to kill orignal server, as one
can't anymore have two servers started at same time on same
data directory and data files.
- Disable maria.small_blocksize as one can't anymore change
aria block size after system tables are created.
- Speed up creation of help tables by using lock tables.
- wsrep_sst_resync now also copies Aria redo logs.
